A large, arcuate seaway that, at its maximum development, extended a distance of 4500 km from just north of the Alps to just east of the Aral Sea. By the end of the Oligocene it had been separated from the Boreal Sea by closure of the Ural, Polish, and Alsace Straits. Towards the end of the Miocene it became more lagoonal in character and by the Pliocene was represented only by a series of land-locked lakes: Lake Balaton in Hungary, the Black Sea (rejoined to the Mediterranean Sea by Quaternary faulting), the Caspian Sea, and the Aral Sea.